Re: 3-blade fixed prop recommendations?
I sail a Marshall Sanderling (Marshall 18) catboat, equipped with a Yanmar 1GM Diesel which originally drove a generic 2-blade Michigan "Sailor" 12 x 10 prop via a 2.62:1 gear. Though the prop was properly matched (it allowed the engine to just reach its intermittent max rpm of 3600 at wide-open throttle), it produced vibration and noise out of proportion to its power. Norm at West By North Enterprises convinced me that there was no sailing advantage to the 2-blade (simple test: I stopped the prop from windmilling with my hand, and there was no change in drag when I had the prop blades vertical), and talked me into trying the Campbell Sailer 3-blade. Right off the bat I noticed far less vibration at all speeds and GALA VI was much easier to back and maneuver (though I still drop the centerboard a few inches). I also won the Catboat Class race at the 2011 Provincetown Schooner Regatta! Only problem was that the engine now topped out at just shy of 3200 rpm. After corresponding with Norm, I took the prop to a local propeller shop over the winter and had a bit of cupping removed from the trailing edge; voila-the engine now maxes out at 3500 (close enough for rhythm & blues) and I cruise the boat at about 5 kts. at 2600-2800 rpm depending on conditions. This leaves plenty of headroom for punching into strong headwinds/seas if necessary, etc. I couldn't be happier with it.